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Some of the consequences for the muscle as a whole are apparent when the mechanical behavior of mus- Most overlap cle is examined in more detail (see Chapter 9) generic alesse 0.18mg visa. The overall shortening is the sum of Events of the Crossbridge Cycle the shortening of the individual sarcomeres discount alesse 0.18mg with visa. Drive Muscle Contraction The process of contraction involves a cyclic interaction be- tween the thick and thin filaments. The steps that comprise amount of force that can be produced, since a shorter the crossbridge cycle are attachment of thick-filament length of thin filaments interdigitates with A band thick fil- crossbridges to sites along the thin filaments, production of aments and fewer crossbridges can be attached. Thus, over a mechanical movement, crossbridge detachment from the this region of lengths, force is directly proportional to the thin filaments, and subsequent reattachment of the cross- degree of overlap. At lengths near the normal resting bridges at different sites along the thin filaments (Fig. Most of our knowledge of this process comes from studies on skeletal muscle, but the same basic steps are followed in all muscle types. Initially, the crossbridges extend at right angles from each thick filament, but they rapidly undergo a 1. An ATP molecule bound to each crossbridge supplies the energy for this step. The myosin head to which the ATP is bound is called “charged myosin” (M*ADP*Pi in step 1). When charged myosin interacts with actin, the association is represented as A*M*ADP*Pi (step 2). The force a muscle can produce depends sociated with the final hydrolysis of the bound ATP and re- on the amount of overlap between the thick and thin filaments lease of the hydrolysis products (step 3), an inorganic phos- because this determines how many crossbridges can interact ef- phate ion (P ) and ADP. An impor- tant series of these steps, called excitation-contraction coupling, takes place deep within a muscle fiber.
Circulatory System © The McGraw−Hill Anatomy buy cheap alesse 0.18mg line, Sixth Edition Body Companies generic 0.18mg alesse fast delivery, 2001 582 Unit 6 Maintenance of the Body TABLE 16. Because the walls of tissues and absorb fats from the gastrointestinal tract. It also is lymphatic capillaries are composed of endothelial cells with part of the body’s defense system against disease. Once fluid Objective 23 Describe the pattern of lymph flow from the enters the lymphatic capillaries, it is referred to as lymph (limf). Objective 24 Describe the general location, histological From merging lymphatic capillaries, the lymph is carried structure, and functions of the lymph nodes. The walls of Objective 25 Describe the location and functions of the lymph ducts are much like those of veins. The pressure that keeps the lymph moving comes The lymphatic system is closely related to the circulatory system, from the massaging action produced by skeletal muscle contrac- both structurally and functionally (fig. A network of lym- tions and intestinal movements, and from peristaltic contrac- phatic vessels drains excess interstitial fluid (the approximate tions of some lymphatic vessels. The valves keep the lymph 15% that has not been returned directly to the capillaries) and moving in one direction. Additionally, the lymphatic the two principal vessels: the thoracic duct and the right lym- system functions in fat absorption and in the body’s defense phatic duct (fig. The larger thoracic duct drains lymph from against microorganisms and other foreign substances. The main trunk of this vessel ascends along the spinal column and drains into the left sub- • It transports excess interstitial (tissue) fluid, which was ini- clavian vein. In the abdominal area, there is a saclike enlargement tially formed as a blood filtrate, back to the blood. The smaller right lymphatic duct drains lymphatic vessels from the • Its cells (called lymphocytes), located in lymphatic tissues, right upper extremity, right thoracic region, and right side of the help provide immunological defenses against disease- head and neck.
Identify two places in the respiratory ventilator) to keep their lungs inflated? List the kinds of epithelial tissues found capillary networks are found proven alesse 0.18 mg. What is the mucus to build up and paralyzes the cilia within the respiratory system and describe function of each of these areas and why that line the respiratory tract order alesse 0.18 mg with mastercard. What protective devices of the respiratory the treatment of certain clinical system guard against pollutants, the conditions? Digestive System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 Digestive System 18 Introduction to the Digestive System 635 Serous Membranes and Tunics of the Gastrointestinal Tract 636 Mouth, Pharynx, and Associated Structures 640 Esophagus and Stomach 648 Small Intestine 652 Large Intestine 656 Liver, Gallbladder, and Pancreas 660 Developmental Exposition: The Digestive System 665 CLINICAL CONSIDERATIONS 669 Clinical Case Study Answer 671 Important Clinical Terminology 672 Chapter Summary 673 Review Activities 674 Clinical Case Study A 25-year-old male construction worker was admitted to the emergency room after suffering a blow to the upper abdomen from a swinging beam. Initial assessment was significant for marked tenderness in the right upper quadrant of the abdomen and for vital signs and examination findings consistent with mild hemorrhagic shock. Intravenous fluids were administered, causing stabilization of vital signs. Peritoneal lavage (see chapter 2, Clinical Case Study) was likewise negative for blood. A CT scan demonstrated a significant hematoma (collection of blood) deep within the substance of the liver (see arrow on CT scan), as well as a notable amount of blood in the small intestine. Initial exploration revealed no trauma to the stomach or small intestine. Explain anatomically how the blood found its way into the small intestine, noting each step of its path. Given that the hepatic arterial system and hepatic venous system are possible sources of the bleeding, is there another system of blood vessels relative to the liver that could also be a source of hemorrhage? FIGURE: Positioned in the upper right quadrant of the abdominal cavity, the liver is Hint: As you study the digestive system, pay close attention to the location of each accessory the largest visceral organ.
This design type may be more efficient or more acceptable when the disease under study is infrequent or when the reference standard procedure is highly invasive to the patient purchase alesse 0.18mg fast delivery, for example in pancreatic cancer safe alesse 0.18 mg, or very expensive. A further approach is test based enrolment, where the available test result (such as positive or negative) is the criterion for recruitment, with the disease status being determined afterwards. This modification may be preferable when test results are easily available from routine health care. An example regarding the latter is a study on the diagnostic value of “fatigue” for detecting anaemia in primary care, comparing patients presenting with fatigue and a control group as to haematological parameters. For example, in order to achieve a balanced data collection over the relevant categories, a stratified sample can be drawn from the various test result levels or from various parts of the whole disease spectrum, from clearly no disease to most severe disease. Also, the contrast between the categories of the diseased and non-diseased subjects can be enhanced by limiting the sampling to those who have been proved to be clearly diseased and those proved to be completely healthy. The latter approach is applied in planning a Phase I study (Chapter 2), which is essentially a case–referent study. Because of a sharp contrast in disease spectrum between diseased and non-diseased, sensitivity and specificity will be optimal, and as by sampling of cases and referents the “prevalence” in the study population can also be artificially optimised (with, for example, a disease prevalence of 50%), Phase I studies generally need a relatively small number of subjects to be included. Moreover, for a Phase I study the subjects in the “case group” (the diseased) and those in the reference group (the healthy or non-diseased subjects) can be specifically selected from populations consisting of subjects who have already undergone a “reference standard” procedure with maximum certainty. Direction of data collection Whereas Phase I and Phase II studies (according to Sackett and Haynes, Chapter 2) may be based on either retrospective or prospective identification of subjects with a certain diagnosis or test status, Phase III studies must usually be prospectively planned. The latter start from a study 44 ASSESSING THE ACCURACY OF DIAGNOSTIC TESTS population of subjects comparable with those who will be tested in clinical practice. In such studies it is not known in advance who is diseased and who is not, and the clinical characteristics of the two are therefore very similar (which in fact is the reason that testing is clinically necessary at all). Because the clinical contrast is much less pronounced, and as the prevalence of diseased subjects is usually much lower than 50%, substantially larger sample sizes are generally needed than in Phase I studies. Also, when the subject selection is prospective the data collection can be partly retrospective (ambispective approach).
